This study is a pilot project by established researchers utilizing innovative techniques that can be used in further investigations of the effects of chronic drug use on nutritional status. The primary objective of this study is to determine if one drug, cimetidine, interferes with the absorption of either the mono- or polyglutamyl form of folacin. Folacin deficiency is a frequent occurrence in the elderly and is often associated with health-related consequences including megaloblastic anemia, malabsorption syndromes, and impaired immune and neurological functions. Cimetidine is the most frequently prescribed drug in the world and results in an elevation of jejunal pH which is hypothesized to interfere with the pH-sensitive folacin absorption mechanism. A triple-lumen jejunal perfusion technique utilizing H3-pteryolmonoglutamyl folacin (H3-PG-1) and C14-pteryolheptaglutamyl folacin (C14-PG-7) will be used to quantitate the effect of either a 0 or 300 mg dose of cimetidine on folacin absorption. Intraluminal pH changes in response to cimetidine or a placebo will be monitored in vivo throughout the perfusion by an electrode positioned in the jejunum. Ten healthy elderly (greater than 65 yrs) white male subjects will serve as their own controls. The relationship between cimetidine use and the development of folacin deficiency in the elderly will be characterized in this study. These data can be used to prevent the development of this debilitating deficiency in elderly cimetidine users.